Rotator Interval

The RTI is an area of shoulder capsule that is bounded by the supraspinatus superiorly, the subscapularis inferiorly, the coracoid process medially, and the long head of the biceps tendon laterally. The floor of the RTI is variably bridged by the GH capsule, the SGHL, the CHL, and occasionally, the MGHL. This area serves as safe portal for arthroscopic entry into the GH joint, because it does not violate the muscles of the RTC.

In a cadaveric study comparing the RTI of fetuses with those of adults, the RTI capsule was found, histologically, to be made of a disorganized system of collagen fibers, and it often contained a congenital hole or defect between the supraspinatus and subscapularis muscles. This evidence suggests that an RTI capsular defect is a normal anatomical variant and not an acquired lesion.

The RTI can thus contribute to inferior instability of the adducted arm. A persistent sulcus sign that does not lessen or disappear with external rotation of the arm suggests a loose or deficient RTI capsule. In patients with multidirectional instability, the RTI is characteristically thinned or absent, and a defect in this area can disrupt the negative intra-articular pressure system that normally exists in the shoulder and contribute further to instability. In contrast, a tight RTI is associated with adhesive capsulitis or postoperative stiffness and may need to be released in order to regain adequate range of motion.

In a biomechanical study using cadaveric specimens, a transverse incision in the RTI allowed for statistically significant increases in humeral head translation in all planes tested. Subsequent imbrication of the RTI decreased inferior translation in adduction and posterior translation in flexion.